The process of learning all about AC motors and what the different type of relays do or don't do came about one day when I found a Baldor bench grinder (model 612E) at a local sale for only $5. I had wanted a grinder like this for a long time by now and at the time had no idea what the Baldor brand was. As soon as my neighbor saw what I had he told me that it was one of if not THE best brand name when it came to shop tools like this. I was pretty excited by this and was eager to see if this thing would work so I headed home to try it out.
My new Baldor 612E grinderStarting the Baldor up for the first time:
Once I got home and plugged in this grinder my joy of finding it went away when it barely wanted to run. Not only did the motor run at very slow RPMs but it ran backwards. I could tell this was running backwards two ways. First this grinder has an exhaust on it and if the wheels were turning the way they did when I turned it on the exhaust would do absolutely no good and your face would be getting all the debris when using it. Second and even easier way to tell was the rotation sticker found on top of the unit. It spun in the opposite direction of this sticker and it spun very slow.
At first I figured the motor must have been shot and that's why I got it for such a low price.
Well time for me to see what's under the hood I guess..I had never taken a part a tool like this so had no idea what to expect and for the cheap price I got it I thought I could go ahead and gamble on fixing this myself.
Taking the Baldor a part:
Surprisingly the screws and bolts all came off very easily so that was a big plus. I figured something that had aged like this one would have at least a few bolts or screws that would want to battle me, but not this time. I did soak them all with PB blaster before taking them out so who knows maybe that's what did the trick.
Anyway now that I have it open I see inside the bottom two units plugged into the AC motor wires.
one of the units was easy to figure out, it was the on off switch. the other thing however took a little researching to figure out and that is actually what prompted this entire article.
Finding out why this runs slow and backwards:
After many many hours of researching online and making posts on a few message boards I finally figured out what was wrong with my grinder and what part I needed to buy in order to fix it.
That second part that I saw under the unit was the problem and at first I thought it was called a Potential Relay but after many more hours of looking for a cheaper replacement part I found an article explaining what the difference is between a potential relay and a current relay. Now I understand quite a bit more and know that I am in need of a current relay to make this work again.
With the help of a few people at the Practical Machinist message board I was able to test the grinder by bypassing the Relay (Current Relay) and when I did this the motor not only spun the correct direction but it went much faster and I assume at the correct RPMs now.
To read the post and see how I bypassed the relay visit:
http://www.practicalmachinist.com/vb/general/seeking-help-replacing-relay-baldor-bench-grinder-another-brand-284723/
This is another great post that explains the difference between the two types of relays plus tells you more about start capacitors, inductive run, resistance etc.:
http://www.refrigeration-engineer.com/forums/showthread.php?7506-Relay-selection
Blurb from that site...
RSIR (Resistive[or Reactance] Start Inductive Run) ...this uses a CURRENT relay.
CSIR (Capacitor Start Inductive Run) ....this uses a CURRENT relay.
CSR (Capacitor Start [ and Capacitor] Run) .....this uses a POTENTIAL relay.
PSC (Permanent Split Capacitor)...no relay required
The holy grail of Articles and information regarding Current Relays or Potential Relays cna be found at:
http://www.hvacrinfo.com/Cope_manuals/ELECTHB.pdf
There is also a cross reference section that you can use to find replacement part numbers for GE relays or Copeland Relays. I was very happy to find this article and never thought to look up refrigeration repairs but I guess that makes sense since they use the same type AC motors.
Mars product Cross reference:
Klixon 3CR107-169 would be a MARS 27006
The MArs 27006 relay has the following specs:
Max Pick-up: 11.8
Min drop out: 9.8
My Baldor grinder has the relay that is made by Texas Instruments (3cr-738-169) and has the following specs:
According to: http://www.carbonbrush.com/3cr.pdf
Max Pick-up: 12.2
Min Drop-out: 10.2
Here is another thread on Yahoo that discusses the Current relay vs Potential Relays:
https://answers.yahoo.com/question/index?qid=20070414045719AAiZTJd
The process of learning all about AC motors and what the different type of relays do or don't do came about one day when I found a Baldor bench grinder (model 612E) at a local sale for only $5. I had wanted a grinder like this for a long time by now and at the time had no idea what the Baldor brand was. As soon as my neighbor saw what I had he told me that it was one of if not THE best brand name when it came to shop tools like this. I was pretty excited by this and was eager to see if this thing would work so I headed home to try it out.
Finding out why this runs slow and backwards:
After many many hours of researching online and making posts on a few message boards I finally figured out what was wrong with my grinder and what part I needed to buy in order to fix it.
That second part that I saw under the unit was the problem and at first I thought it was called a Potential Relay but after many more hours of looking for a cheaper replacement part I found an article explaining what the difference is between a potential relay and a current relay. Now I understand quite a bit more and know that I am in need of a current relay to make this work again.
With the help of a few people at the Practical Machinist message board I was able to test the grinder by bypassing the Relay (Current Relay) and when I did this the motor not only spun the correct direction but it went much faster and I assume at the correct RPMs now.
To read the post and see how I bypassed the relay visit:
http://www.practicalmachinist.com/vb/general/seeking-help-replacing-relay-baldor-bench-grinder-another-brand-284723/
This is another great post that explains the difference between the two types of relays plus tells you more about start capacitors, inductive run, resistance etc.:
http://www.refrigeration-engineer.com/forums/showthread.php?7506-Relay-selection
Blurb from that site...
RSIR (Resistive[or Reactance] Start Inductive Run) ...this uses a CURRENT relay.
CSIR (Capacitor Start Inductive Run) ....this uses a CURRENT relay.
CSR (Capacitor Start [ and Capacitor] Run) .....this uses a POTENTIAL relay.
PSC (Permanent Split Capacitor)...no relay required
The holy grail of Articles and information regarding Current Relays or Potential Relays cna be found at:
http://www.hvacrinfo.com/Cope_manuals/ELECTHB.pdf
There is also a cross reference section that you can use to find replacement part numbers for GE relays or Copeland Relays. I was very happy to find this article and never thought to look up refrigeration repairs but I guess that makes sense since they use the same type AC motors.
Mars product Cross reference:
Klixon 3CR107-169 would be a MARS 27006
The MArs 27006 relay has the following specs:
Max Pick-up: 11.8
Min drop out: 9.8
My Baldor grinder has the relay that is made by Texas Instruments (3cr-738-169) and has the following specs:
According to: http://www.carbonbrush.com/3cr.pdf
Max Pick-up: 12.2
Min Drop-out: 10.2
Here is another thread on Yahoo that discusses the Current relay vs Potential Relays:
https://answers.yahoo.com/question/index?qid=20070414045719AAiZTJd